In the production process for semiconductor devices, such as ICs and LSIs, it is conventional practice to perform microfabrication by lithography using a photoresist composition. In recent years, the formation of an ultrafine pattern in the submicron region or quarter-micron region is increasingly demanded in accordance with the realization of high integration for integrated circuits. Accordingly, the trend of exposure wavelength toward a short wavelength, for example, from g-rays to i-rays and further to KrF excimer laser light is seen.
Resist compositions for KrF comprising a resin whose fundamental skeleton consists of a poly(hydroxystyrene) have been developed. As such a resin, it is known to use, for example, a copolymer from hydroxystyrene and a monomer containing an adamantyl group (see, for example, patent reference 1).
In contrast, as resist compositions for which mainly an ArF light source is used, those comprising a resin containing no aromatic ring have been developed. For example, compositions comprising a resin with a specified lactone structure are known (see, for example, patent reference 2). Moreover, as a photoacid generator of high transmission, it was reported to use an alkyl aryl onium salt (see, for example, patent references 3 and 4).
Meanwhile, it was reported to use compounds having a basic moiety, each of which when exposed to radiation, generates an acid to thereby have its basicity lowered or become neutral, with the intent to attain an enhancement of pattern profile, line edge roughness or the like (see, for example, patent references 5 and 6).
As a result of the inventors' study, it has become apparent that the use of a compound having a basic moiety that when exposed to radiation, generates an acid to thereby have its basicity lowered or become neutral is likely to cause the resist composition to be unstable.